bios option rom to provide legacy serial console for x86

 The Google Serial Graphics Adapter BIOS or SGABIOS provides a means for
 legacy x86 software to communicate with an attached serial console as if
 a video card were attached. SGABIOS is designed to be inserted into a BIOS
 as an option rom to provide over a serial port the display and input
 capabilities normally handled by a VGA adapter and a keyboard. SGABIOS
 can be used to feature OS independent serial console redirection in Qemu.